1. Field of the Invention
The invention generally relates to systems in which audio content is transmitted between entities. In particular, the invention relates to systems in which audio content is wirelessly delivered from a single audio source to two audio sinks.
2. Background
In the past, telephone communication and the consumption of media content required a user to be stationary, since the electronic devices and systems that enabled such activities were themselves stationary. However, with advances in mobile technology, telephone users and media consumers have become mobile as well. The use of cellular telephones for mobile communication has become ubiquitous. Additionally, a wide variety of portable electronic devices are now available that can be used to store or access media content for playback at virtually any location. Such devices include but are not limited to portable media players, handheld computing devices, laptop computers and media-enabled cellular telephones.
To meet the demands of mobility, the speakers associated with such cellular telephones and portable electronic devices are often small and designed to operate using little power. This places constraints on the loudness and quality of the audio that can be produced by such devices. Additionally, some portable electronic devices have no speakers at all, but instead require the use of headphones to listen to audio content. Users may also choose to use headphones with devices that do have a speaker (such as cellular telephones) to enhance their perception of the audio content, to free up their hands, and/or to prevent others from hearing the audio. In any case, if the headphones are wired, then the user must be physically tethered to the device, which can be inconvenient and/or uncomfortable.
To address these issues, technology has been developed that allows cellular telephones and other portable electronic devices to form wireless links with external speaker systems so that the portable electronic devices can deliver audio content over the external systems. Examples of such external speaker systems include wireless headphones and headsets, stand-alone wireless speakers, or speakers integrated within other electronic devices or systems that are adapted to receive audio wirelessly. Protocols that can be used to enable the wireless streaming of audio to such systems include but are not limited to the well-known protocols for short-range wireless communication defined in the Bluetooth™ specifications (developed and licensed by the Bluetooth™ Special Interest Group) and the well-known protocols for wireless local area network (WLAN) communication defined in the various IEEE 802.11 standards (developed by the IEEE LAN/MAN Standards Committee).
One type of external speaker system to which audio content may be delivered wirelessly is a stereo speaker system that includes a left-channel speaker and a right-channel speaker. A conventional approach to wirelessly delivering audio content to such a system is depicted in FIG. 1. In particular, FIG. 1 is a block diagram of a conventional system 100 in which an audio source 102 wirelessly delivers audio content to a first audio sink 104 and a second audio sink 106, wherein the audio sinks are connected by a wired link 110. First audio sink 104 and second audio sink 106 are intended to represent audio speakers, or devices that contain such speakers. In system 100, audio source 102 transmits an audio stream 112 over a wireless link 108 to first audio sink 104. First audio sink 104 receives the audio stream and extracts two channels of audio content therefrom—namely, a left audio channel and a right audio channel. One channel is played back by first audio sink 104, while the other channel is transmitted over wired link 110 for playback by second audio sink 106.
In the approach shown in FIG. 1, the respective playback of each of the two channels of audio content by first audio sink 104 and second audio sink 106 can be highly synchronized since first audio sink 104 manages both channels of audio content and the delivery of audio content from first audio sink 104 to second audio sink 106 takes place over a wired transmission medium. Furthermore, the quality of the audio produced by second audio sink 106 will likely be as good as the quality of the audio produced by first audio sink 104 since little or no packet loss is expected over wired link 110. However, the approach shown in FIG. 1 is limiting because it requires that first audio sink 104 and second audio sink 106 be physically connected to each other by wired link 110. This limits the placement and mobility of each of the audio sinks. Furthermore, this prevents audio source 102 from establishing ad hoc links with two speakers that are not part of the same speaker system.
Another conventional approach to wirelessly delivering audio content to a stereo speaker system is depicted in FIG. 2. In particular, FIG. 2 is a block diagram of a conventional system 200 in which an audio source 202 wirelessly delivers audio content to a first audio sink 204 and a second audio sink 206, wherein the audio sinks are communicatively connected to each other via a wireless link 210. In system 200, audio source 202 transmits a first audio stream 212 over a wireless link 208 to first audio sink 204. First audio sink 204 receives first audio stream 212 and extracts two channels of audio content therefrom. One channel is played back by first audio sink 204, while the other channel is transmitted to second audio sink 206 as part of a second audio stream 214 transmitted over wireless link 210. Second audio sink 206 receives the second audio stream 214 and extracts the other channel of audio content for playback.
The approach shown in FIG. 2 is advantageous in that it does not require a wired link between first audio sink 204 and second audio sink 206. However, this approach also suffers from some drawbacks. For example, in the approach shown in FIG. 2, if wireless link 208 between audio source 202 and first audio sink 204 is degraded for any reason, then the quality of the audio produced by both first audio sink 204 and second audio sink 206 will suffer. Furthermore, if wireless link 210 between first audio sink 204 and second audio sink 206 is degraded for any reason, then the quality of the audio produced by second audio sink 206 will suffer.
Accordingly, what is needed is an approach to delivering audio content from a single audio source to two audio sinks that addresses the foregoing shortcomings associated with conventional solutions.